SUMMARY Chronic inflammatory diseases and oxidative stress are major risk factors of colorectal cancer (CRC), the second-ranked cause of death among cancer patients. However, the mechanisms through which increased oxidative stress and inflammatory markers cause CRC are not well understood. Understanding these biochemical mechanisms, especially the role of increased reactive oxygen species (ROS) in the pathophysiology of CRC, will help in developing better therapeutic strategies. We have recently demonstrated that aldose reductase (AR) an enzyme that we have shown catalyzes the reduction of ROS- induced lipid aldehydes and their glutathione-conjugates (such as HNE and GS-HNE to DHN and GS-DHN), is an obligatory mediator of growth factor and cytokine-induced NF-B activation in human colon cancer cells. Further, we have shown that AR inhibition or ablation by SiRNA prevents the growth of colon cancer cells in culture as well as in nude mice xenografts. Our long term goal is to understand the mechanisms by which AR contributes to CRC progression, and to develop AR inhibitors (ARIs) for chemoprevention of CRC. We will now systematically examine our hypothesis that the effects of ROS are in part mediated by AR- catalyzed reduced lipid peroxidation-derived aldehydes (LDAs) and their metabolites by investigating the role of AR in mediating growth factor-induced cancer growth in cultured cells, nude mice xenografts and murine models of CRC. Our specific aims are 1) Investigate the effects of AR inhibition on the growth factor-induced progression of cultured human colon cancer cell growth, 2) Delineate the effects of AR inhibition/ablation on colon cancer progression in nude mouse xenografts, and 3) Delineate the chemopreventive efficacy of AR inhibition in chemically and genetically-induced CRC in murine models. Completion of these studies should identify the molecular mechanisms of AR- reduced LDAs in mediating carcinogenic signals, and lead to use of AR inhibitors as excellent chemopreventive drugs for CRC.